In many prior art methods of embossing designs, such as stitching, onto a thermoplastic sheet, both the anvil surface and the embossing die surface were rigid and hard. In addition, the anvil surface was typically flat. The combination of the hard flat anvil surface and the hard embossing die surface provided an uneven distribution of pressure on the thin thermoplastic sheet, as it was being formed, and this often produced distortions in the thickness of the sheet. Furthermore, to form raised bosses on the surface of the sheet, it was necessary to force the material to plastically flow from the high pressure debossing areas into the low pressure embossing regions. This required high temperatures, high pressures, and in general, dictated that the process be closely controlled because there was always the danger of projecting features on the die cutting through the thermoplastic sheet.
Some improvement in the embossed pattern is achieved by using an unrestrained slab of elastomer as the embossing anvil. The elastomeric slab is intended to react to the pressure of the embossing die by undergoing a displacement such that the hot plastic sheet is more uniformly and completely forced into contact with the embossing die.
The decorative coating of embossed designs presents many problems, not the least of which is the cost of separate preparatory steps such as masking. Often these problems were solved by simply avoiding liquid painting (i.e., coating) methods and using transfer type coating techniques. The subject invention solves these problems and provides a simple economical method of forming an attractive coated and embossed design in one operation. We have found that the subject coating method is particularly effective in combination with embossing techniques that employ an elastomeric anvil. Preferably, the anvil is laterally restrained so that it is not pushed from under the embossing die.
Hereinafter the term embossing is used to denote the overall process of impressing a design onto a formable sheet, wherein said design may have both raised and lowered features.